Snap action device



March 24, 1959 J. w. WELSH 2,879,355

SNAP ACTION DEVICE Filed June s, 195'? 2 Sheets-Sheet 1 FIG.1

I J l FIG. 2

INVENTOR.

ATTORNEY March 24, 1959 J. w. WELSH SNAP ACTION DEVICE 2 Sheets-Sheet 2Filed June 6, 1957 FIGS 9 LZV%TOR.

ATTORNEY SNAP ACTION DEVICE James W. Welsh, Summit, N.J., assignor, bymesne assignments, to Hoda Corporation, Great Neck, N.Y., a corporationof New York Application June 6, 1957, Serial No. 664,034

9 Claims- (Cl. 200113) This invention relates to electric switches orcircuit controllers using a snap action vane actuated by a thermostaticor thermodynamic opera-tor to control the operation of circuitcontrolling contacts. More particularly, the invention is directed toswitches of this type in which the thermostatic operator is an integralor unitary part of the snap action vane.

In my US. Patent No. 2,756,304 of July 24, 1956, I have illustrated anddescribed a novel type of snap action vane, and a switch or flasherincorporating the same, in which a vane of relatively stifi spring metal'is given an initial set by providing a pair of aligned andlongitudinally spaced deformations extending from diagonally oppositecorners of the vane toward the center thereof, the central area of thevane being left undeformed. This gives the vane an initial bend about afirst diagonal extending along the deformation.

The vane is pre-stressed to bend about the other diagonal by attaching athermostatic wire or ribbon to the corners at the ends of the firstdiagonal, the wire or rib bon being attached in the cold, contractedcondition with the vane bent about the second diagonal. When the wire orribbon is heated and expands, the vane snaps to its initial bentcondition about the first diagonal. When the Wire or ribbon cools andcontracts, the vane snaps back to its condition of being bent about thesecond diagonal.

If such a vane is supported in a certain zone adjacent its center, thereis a considerable amplitude of movement of the vane about such mountingpoint during the snapping action, particularly at the corners of thevane. This characteristic has been advantageously utilized in providingvane-operated switches controlling circuits preferably includingelectric heating circuits for the thermostatic operator, and flashers orother snap action switches incorporating such a vane have gone intoextensive commercial use.

In accordance with the present invention, it has been found that themanufacture of such snap action vane switches can be greatly simplifiedand reduced in cost by making the thermostatic operator integral withthe vane in a single vane forming operation. This eliminates the timeand labor hitherto necessary in pre-stressing the vane and holding itpro-stressed while the pull ribbon or wire is attachedto the Vane byspot welding or brazing. Even more importantly, the contact making andbreaking operation of the vane is greatly improved, as the contactpressure is maintained fully or even increased during a contact openingcycle right up to the instant when the contacts snap open. Thischaracteristic greatly increases the contact life by minimizing arcingor burning of the contacts.

In making the vane, a piece of preferably electrically conductive springmetal is used, the metal being selected for high elasticity andresistance to creep under static or dynamic stresses. Other factorsimportant in the selection of the metal are its specific temperatureresistance, coefficient of electrical resistance, and coefiicient ofexpansion, all of which factors must be considered with paratent ticularreference to external or ambient operating conditions.

The metal piece is formed with a closed-end slot extending along andparallel to an edge so as to provide a narrow strip of metal along suchedge integral at each end with the much larger main body section of thevane. At least the main body section of the vane is then deformed into ashallow V-shape with the apex of the V extending perpendicularly to thenarrow strip and preferably bisecting the latter. Such deformation maybe effected by providing or forming a narrow rectangular flat sectionalong such apex, with the wings of the V extending at a small angle tosuch section.

If the main body of the vane is now fixedly supported at a point alongor immediately adjacent the apex of the V, and the vane is heated, as bypassage of an electric current therethrough, the narrow strip along thevane edge, due to its much smaller cross-section, will expandlongitudinally at a rate much greater than the rate of expansion of themain body of the vane. Such expansion of the thermostatic operator orstrip results in outward forces on the main body at the junctures of thestrip thereto, and this tends to flatten the V. Suchfiattening, in turn,tends to lower the strip relative to the vane mounting point and, ifsuch lowering is resisted as explained hereinafter, further heating andexpansion of the strip causes the latter to snap to an upwardly bowedposition. If the heating is now dsicontinued, the heater wire section ofthe vane cools and the resulting contraction of the strip brings thematerial to its new equilibrium point and thus snaps the latter back toits original position.

As applied to an electric switch, a first contact secured on theundersurface of the strip at or immediately adjacent its mid-section isnormally engaged with a second contact fixed relative to the vanemounting point, these two contacts forming part of an electric heatingcircuit including the vane. When this circuit is closed, with resultantheating of the vane due to electric current flow therethrough andconsequent expansion of the integral strip as explained above, thesecond contact resists or prevents lowering of the strip relative to thevane mounting point. Thus the contact pressure is maintained and evenincreased during the heating cycle right up to the instant the stripsnaps to the upwardly bowed position disengaging the contacts andopening the heating circuit. This maintenance of the contact pressure,in combination with the snap opening of the contacts, greatly prolongsthe contact life. Such prolongation of contact life is enhanced by thesnap re-closing of the contacts.

The vane may have any desired shape in plan, such as a square, arectangle, a circle, or a semicircle, dependent upon the desiredparameters and intended use of the switch.

For an understanding of the invention principles, reference is made tothe following description of typical embodiments thereof as illustratedin the accompanying drawings. In the drawings:

Figs. 1, 2 and 3 are plan views of three pieces of metal slotted to formsnap action vanes in accordance with the invention but beforedeformation of the main body into a shallow V-shape;

Fig. 4 is a plan view of the vane of Fig. 1 after deformation of themain body of the vane;

Fig. 5 is a side elevation view of the vane of Fig. 4, the V-shape ofthe main body being exaggerated;

Fig. 6 is a bottom plan view of the vane attached to a mounting bracketcarrying, in insulated relation, a contact engageable with a contact onthe undersurface of the strip;

Fig. 7 is a front elevation view of an automotive type flasher unitembodying the vane of Figs. 1 and 4, the circuit controlled therebybeing schematically illustrated;

Fig. 8 is a side elevation view of the flasher unit; and

Fig. 9 is a view similar to Fig. 7 showing the flasher contacts open.Referring to Fig. 1, a vane 15, in accordance with the invention, may beformed by taking a rectangular piece of thin, relatively stifi,resilient metal and forming a. closed-end slot 16 along one edge so asto divide the vane into a relatively narrow thermostatic operator strip20 integral at each end with a main body section 21. The metalpreferably has highelectrical resistance.

While, for most applications, a rectangular shape vane is desirable, thevane shape is dictated by external parameters. In some cases a circularor semicircular shape, such as the vane 15' of Fig. 2 or the vane 15" ofFig. 3 is desirable. Vanes of circular or semi-circular shape may beuseful, for example, as circuit breakers installed in lamp sockets. Insome other instances, a square shape or an, arcuate shape may bepreferred.

Irrespective of the shape of the vane, the cutting of the slot 16 (16',16") provides a narrow thermostatic operator strip 20 (20', 20") alongan edge of the vane and separated by the slot from the main body section21 (21', 21") of the vane. This strip, which is integral with the mainbody section at each end 17 (17, 17"), has a cross-sectional area only afraction of that of the main section, and acts as the usual resistancewire or strip hitherto separate from and mechanically attached to thevane along a diagonal.

Either during the formation of slot 16, or after the slot is formed, thevane, preferably including strip 20, is given a shallow V-shape with theapex 22 of the V extending normal to strip 20 and preferably bisectingthe latter. This may be efiectively accomplished by providing arectangular flat section 23 along the apex of the V as shown in Fig. 4.The angle of the V in section 21 is greater than any angle of the V instrip 20.

For effective action of vane 15 as a snap action switch, body section 21must be secured or supported at a fixed point on or immediately adjacentthe apex of the V. Referring to Fig. 6, this is accomplished, inpractice, by spot welding or brazing section 21 to one end 31 of anelectrically conductive bracket 30 having a center section 32 ofi'setvertically from end 31 and extending beneath strip 20. Bracket 30 has anouter end 33 offset vertically from mid-section 32. Mid-section 32 has aband 34 of dielectric material therearound, and astrip 36 of conductivematerial is wound about band 34 and carries a contact 35 normallyengaged with a contact 25 on the undersurface of strip 30.

To form a flasher, the vane and bracket combination 15-30 is mounted ona dielectric base 40 carrying receptacle engaging prongs 41, 42, asshown in Figs. 7-9. In this assembly, the outer end 33 of bracket 30 iswelded, brazed, or soldered to a rivet securing prong 41 to base 40, andthe outer end of conductor 36 is welded, brazed or soldered to a rivetsecuring prong 42 to base 40. In making this assembly, the mechanics ofassembly are such that strip 20 has a shallow V-shape'and firmly pressesits contact 25 against the contact 35 mounted in insulated relation onthe mid-section 32 of bracket 30.

' Before describing the operation of the vane, reference is made to theschematic wiring diagram of Fig. 7. As therein illustrated, one terminalof agrounded battery 43, which may be an automotive battery, isconnected through a switch 45 to a receptacle (not shown) in which prong41 is engaged. Prong 42 is engaged in a receptacle (not shown) connectedto a grounded load such as lamps 44. When switch 45 is closed, currentwill flow from battery 43 to prong 41, bracket 30, and vane 15. Thecurrent in vane 15 flows over two parallel paths to the opposite ends ofstrip 20, through the strip and closed contacts 25, 35 and thence intostrip 36, from whence the circuit is completed through prong .42 andlamps 44 to ground.

- As strip 20 has a cross-section much less than that of body section21, it is heated much more rapidly than the 4 body section, when theheating circuit is completed by closing switch 45. Consequently strip 20expands longitudinally relative to body "section 21. As strip 20expands, it is restrained at its ends by the V-shape body 21, so thatthe center of strip 20 is forced downwardly to increase the pressure ofcontact 25 against fixed contact 35. The continued expansion of strip20, with downward movement of the strip thus-restrained, results in astraightening force being exerted on body section 21.

This results in a toggle action wherein, when the out ward force ofstrip 20 and the constraint exerted by section 21 reach an equilibriumpoint, strip 20 is snapped to an upwardly bowed position as shown inFig. 9. This results in a snap separation of contacts 25-35 which, untilthe exact moment when they are snapped apart, are maintained underincreasing contact pressure. The toggle action resulting in snapping ofstrip :20 to a new position is due to the inward force of section 21 onthe ends of strip 20 asa result of section 21 tending to return to itsinitial V-shape.

When contacts 25-35 are thus snapped apart, the heating circuit isopened and strip 20 starts to cool and contract. As strip 20 passesthrough the equilibrium point, the pressure of section 21 on its endssnaps strip 20 back to the position of Figs. 7 and8, thus re-engagingcontacts 25-35 witha snap action and under the initial contact pressure.j

While specific embodiments of the invention have been shown anddescribed in detail to illustrate the application of the inventionprinciples, it will be understood that the invention may be embodiedotherwise without departin from such principles.

What is claimed is: I r i 1. In an electric switch, a snap action vanecomprising a substantially flat piece of a single resilient metal havinga relatively elongated closed-end slot extending along and adjacent anedge thereof to divide the vane into a main body section anda-strip-separatedfrom said body section by said slot and integral withthe body section at each end, with the strip having a cross-sectionalarea only a fraction of that of the body section; whereby, upon cyclicheating and cooling of said strip the latter will cyclically expand andcontract-relative to the body section and, due to the reaction of thebody section on the ends of the strip, the intermediate portion of thestrip will move substantially, relative to the body section, out ofco-planar relation with the latter; an electric heating circuit for saidstripincluding said strip;.afixed support secured to said body section;-a first contact fixed relative to said support; and a second contactcarried by said strip and movable into and .out of engagement with saidfirst contact by such relative movement of said strip. x i

2. In an electric switch, a snap action vane comprising a substantiallyflat piece of a single resilient metal of relatively high electricalresistance having a relatively elongated closed-end slot extending alongand adjacent an edge thereof to divide the vane into a main body sectionand a strip separated from said body section by said slot and integralwith the body section at each end,

with the strip having a cross-sectional area only a fracportion' of thestrip will move substantially relative to 1 the body section, out ofco-planar relation with the latter;

a fixed support secured to said body section; a first contact fixedrelative to said support; a second contact carried by said strip andmovable into and out of engagement with said first contact by suchrelative movement of said strip; and an electric heating circuit forsaid strip including said contacts and said strip.

3. A snap action vane comprising a substantially fiat piece of a singleresilient metal having a single relatively elongated closed-end slotextending along and adjacent one edge thereof to divide the vane into amain body ection and a strip separated from said body section by saidslot and integral with the body section at each end, with the striphaving a cross-sectional area only a fraction of that of the bodysection; at least the main body section of said vane being bent to forma shallow V; whereby, upon heating of said strip the latter will expandrelative to the body section and, due to the reaction of the bodysection on the ends of the strip, the intermediate portion of the stripwill move substantially relative to the body section.

4. A snap action vane comprising a substantially fiat piece of a singleresilient metal having a single relatively elongated closed-end slotextending along and adjacent one edge thereof to divide the vane into amain body section and a strip separated from said body section by saidslot and integral with the body section at each end, with the striphaving a cross-sectional area only a fraction of that of the bodysection; at least the main body section of said vane being bent to forma shallow V having an apex extending normal to said strip; whereby, uponheating of said strip the latter will expand relative to the bodysection and, due to the reaction of the body section on the ends of thestrip, the intermediate portion of the strip will move substantiallyrelative to the body section.

5. A snap action vane comprising a substantially flat piece of a singleresilient metal having a single relatively elongated closed-end slotextending along and adjacent one edge thereof to divide the vane into amain body section and a strip separated from said body section by saidslot and integral with the body section at each end, with the striphaving a cross-sectional area onlya fraction of that of the bodysection; at least the main body section of said vane being bent to forma shallow V having an apex extending normal to said strip andsubstantially bisecting said strip; whereby, upon heating of said stripthe latter will expand relative to the body section and, due to thereaction of the body section on the ends of the strip, the intermediateportion of the strip will move substantially relative to the bodysection.

6. In an electric switch, a snap action vane comprising a substantiallyflat piece of a single resilient metal having a relatively elongatedclosed-end slot extending along and adjacent an edge thereof to dividethe vane into a main body section and a strip separated from said bodysection by said slot and integral with the body section at each end,with the strip having a cross-sectional area only a fraction of that ofthe body section; at least the main body section of said vane being bentto form a shallow V; whereby, upon cyclic heating and cooling of saidstrip the latter will cyclically expand and contract relative to thebody section and, due to the reaction of the body section on the ends ofthe strip, the intermediate portion of the strip will move substantiallyrelative to the body section; a fixed support secured to said bodysection substantially at the apex of the V; a fixed support secured tosaid body section; a first contact fixed relative to said support; and asecond contact carried by said strip and movable into and out ofengagement with said first contact by such relative movement of saidstrip.

7. In an electric switch, a snap action vane comprising a substantiallyflat piece of a single resilient metal of relatively high electricalresistance having a relatively elongated closed-end slot extending alongand adjacent an edge thereof to divide the vane into a main body sectionand a strip separated from said body section by said slot and integralwith the body section at each end, with the strip having across-sectional area only a fraction of that of the body section; atleast the main body section of said vane being bent to form a shallow V;whereby, upon flow of electric current through the strip, the strip willheat and expand relatively to the body section and will cool andcontract relative to the body section when the current flow isinterrupted and, due to the reaction of the body section on the ends ofthe strip, the intermediate portion of the strip will move substantiallyrela' tive to the body section; a fixed support secured to said bodysection substantially at the apex of the V; a first contact fixedrelative to said support; a second contact carried by said strip andmoveable into and out of engagement with said first contact by suchrelative movement of said strip; and an electric heating circuit forsaid strip including said contacts.

8. In an electric switch, a snap action vane comprising a substantiallyflat piece of a single resilient metal of relatively high electricalresistance having a relatively elongated closed-end slot extending alongand adjacent an edge thereof to divide the vane into a main body sectionand a strip separated from said body section by said slot and integralwith the body section at each end, with the strip having across-sectional area only a fraction of that of the body section; atleast the main body section of said vane being bent to form a shallow Vhaving an apex extending normal to said strip; whereby, upon flow ofelectric current through the strip, the strip will heat and expandrelatively to the body section and will cool and contract relative tothe body section when the current flow is interrupted and, due to thereaction of the body section on the ends of the strip, the intermediateportion of the strip will move substantially relative to the bodysection; a fixed support secured to said body section substantially atthe apex of the V; a first contact fixed relative to said support; asecond contact carried by said strip and moveable into and out ofengagement with said first contact by such relative movement of saidstrip; and an electric heating circuit for said strip including saidcontacts.

9. In an electric switch, a snap action vane comprising a substantiallyflat piece of a single resilient metal of relatively high electricalresistance having a relatively elongated closed-end slot extending alongand adjacent an edge thereof to divide the vane into a main body sectionand a strip separated from said body section by said slot and integralwith the body section at each end, with the strip having across-sectional area only a fraction of that of the body section; atleast the main body section of said vane being bent to form a shallow Vhaving an apex extending normal to said strip and substantiallybisecting said strip; whereby, upon flow of electric current through thestrip, the strip will heat and expand relatively to the body section andwill cool and contract relative to the body section when the currentflow is interrupted and, due to the reaction of the body section on theends of the strip, the intermediate portion of the strip will movesubstantially relative to the body section; a fixed support secured tosaid body section substantially at the apex of the V; a first contactfixed relative to said support; a second contact carried by said stripand moveable into and out of engagement with said first contact by suchrelative movement of said strip; and an electric heating circuit forsaid strip including said contacts.

References Cited in the file of this patent UNITED STATES PATENTS2,363,280 Arnold Nov. 21, 1944 2,425,717 Bean Aug. 19, 1947 2,533,274Matulaitis et al. Dec. 12, 1950 2,708,697 Welsh May 17, 1955 2,716,682Franklin Aug. 30, 1955 2,720,568 Bletz Oct. 11, 1955 2,825,960 ProtzMar. 11, 1958 2,834,853 Hood May 13, 1958

